Cape Times – While there is always some seismic risk, authorities do not believe there is a real threat of a mega earthquake of seven or more on the Richter scale in the region.
This after a number of seismic events were recorded in or near Cape Town at the weekend, with no reports of casualties or damage to infrastructure, and no tsunami warning issued.
They also do not pose a risk to the Koeberg Nuclear Power Station which was built to much higher earthquake and tsunami specifications than Japan’s Fukushima.
On Saturday, at 7.10pm, a magnitude 6.2 earthquake struck about 1 600km south-east of South Africa.
The Council of Geoscience (CGS), at around 8.41pm that day, also recorded an earthquake registering a preliminary 2.5 on the local magnitude scale near Durbanville.
“Many reports have been received from residents of Cape Town who have reportedly experienced a tremor during this time.
“It does not seem to be related to the earthquake that occurred at 7.10pm off the coast of South Africa.”
Yesterday, the CGS confirmed a second earth tremor in the same area, at 9.12am.
“The earthquake registered a preliminary 2.3 on the local magnitude scale. The epicentre was located around 5-6km north of Durbanville.
“Reports have been coming in from residents in the Cape Town area who have felt the tremors, although not as widespread as last night’s.
’’These events might be related as they seem to occur in the same area. The CGS would like to appeal to the public to not panic.”
The Western Cape Disaster Management Centre said yesterday it was in contact with the Council of Geoscience, the National Disaster Management Centre and other partners who were jointly monitoring the situation.
The Western Cape Provincial Disaster Management Centre and the City’s Disaster Risk Centre are still activated for Covid-19 and are on standby for any disasters.
Local Government, Environmental Affairs and Development Planning MEC Anton Bredell said South Africa was fortunate in the fact that the continent was on a very stable tectonic plate.
“Our risk for earthquakes and tsunamis is very low. While there is always some seismic risk, we don’t believe there is a real threat for a mega earthquake of seven or more on the Richter scale in the Western Cape.
’’While we can never rule it out completely, the science doesn’t support it. It also bears noting that a 7 on the Richter scale is considered to be 33 times stronger than a 6.”
Bredell said the province had 160 highly trained urban search and rescue technicians who could be called on at short notice to respond to a major disaster.
Nuclear physicist and former South African Nuclear Energy Corporation (Necsa) chair Dr Kelvin Kemm said the Koeberg Nuclear Power Station was built to much higher earthquake and tsunami specifications than Fukushima.
“Koeberg is designed to withstand 7.5 on the Richter scale. The earthquake in the ocean is reported as only 6.2, so Koeberg could withstand a ‘quake’ of over 10 times larger than that,” he said.
When Koeberg was built, all the sand on site was removed down to the bedrock, Kemm added.
“A mixture of sand and cement was then laid about 5m deep. Then about 3m of concrete was laid on top of that. Then on top of the concrete the anti-earthquake system was built.
“It is a set of Bronze-Beryllium plates which can move sideways. The concrete and steel foundation for the reactors was then built on top of this ‘plate chamber.’
“In the event that an earthquake strikes, the lower foundation moves and the reactor building ‘stays behind’ momentarily, and then slowly moves to catch up, because the metal plates allow for lateral movement.
“The nuclear operating defences in the Koeberg reactor system are so advanced that the slightest radiation release that could occur would be detected by a multiplicity of defence systems,” Kemm added.
Roshan Bachan from Tygerdal, Goodwood, said he was watching TV with his family when they heard a growing rumble. “It sounded like it was approaching.
’’And then we felt a vibration, I immediately looked at my wife and said that it was an earthquake. My wife thought it was an explosion. It lasted between five and seven seconds.”
Yesterday morning, he said, the sound and vibration seemed louder and stronger. “The vibration went through the ground and the bed started shaking, the windows were rattling. It probably lasted under 10 seconds. I’ve been around navy firepower and experienced intense thunderstorms, but nothing like that.”
UWC Department of Earth Science senior lecturer Dr Russel Bailie said according to his understanding, there was no local active warning system for tremors and earthquakes.
“Plate tectonics is an active process so South America and Africa are still moving away from each other. The Earth’s crust has to adjust to that and hence earthquakes occur from time to time, like in the 1969 Tulbagh earthquake.”